1. Field of the Invention
The present invention relates to a tilt-trim device for a marine propulsion unit preferably used in an outboard motor or an inboard engine.
2. Description of the Prior Art
A marine propulsion device such as an outboard motor includes a propulsion unit comprising a propeller and an engine supported axially by a swivel bracket such that a horizontal swinging movement is allowed, with the swivel bracket being supported by a clamp bracket to provided a vertical tilting movement, with the clamp bracket gripping the hull. A tilt-trim device is provided between the clamp bracket and the swivel bracket such that the propulsion unit and the swivel bracket are tilted vertically with respect to the clamp bracket by a telescopic motion of a hydraulic cylinder of the tilt-trim device, so as to allow tilt or trim operation of the propulsion unit.
As an example of a tilt device, Japanese Patent Application Laid-Open (JP-A) No. 6-344982 discloses one having a piston connected to one end of a piston rod provided slidably in a cylinder of a cylinder housing such that the inside of the cylinder is divided into a piston side space and a rod side space. A boosting housing is provided slidably at the outer periphery of the cylinder housing so that the boosting housing forms a boosting space and contacts with the piston rod for supplying a hydraulic fluid from a hydraulic fluid supplying and exhausting device to a piston side space and the boosting space for the trim-up and tilt-up operation of the propulsion unit, and for supplying the hydraulic fluid from the hydraulic fluid supplying and exhausting device to a rod side space for the tilt-down and trim-down operation of the propulsion unit.
In the prior art referred to hydraulic fluid is supplied to the piston side space for applying pressure to the piston rod toward the projecting direction via the piston as well as the boosting housing contacts with the piston rod by the hydraulic fluid supply to the boosting space for applying pressure also to the piston rod toward the projecting direction so that the sum of the pressure functions on the piston rod as a large trim-up force.
However, in this prior art, since the channel for supplying and exhausting hydraulic fluid from the hydraulic fluid supplying and exhausting device to the boosting space is exposed outside, the exposed piping prevents downsizing of the tilt-trim device.